Flat or low-slope roofs are often covered with multi-layered roofing systems. These roofing systems often include a roof deck, an insulation layer, and a protective, weather-resistant membrane. In some situations, a coverboard is also employed. In many situations, insulation boards are typically adhered directly to a roof deck, which is most commonly constructed of concrete or steel. These insulation boards are typically closed-cell foams that include polyurethane or polyisocyanurate cellular materials with an insulating gas trapped within the cells. The insulation boards are then covered with the weather resistant membrane.
The foam insulation boards are typically low density cellular structures. The low density stems from two primary considerations. The first is cost because lower density cellular structures employ less material. Also, and often more important, the insulation value of the board can be improved with lower density structures. While a density of zero would be ideal (i.e., a vacuum), a certain degree of cellular structure—which gives rise to the density—is required to maintain the integrity of the insulation boards. Particularly, a foam core density of greater than about 1.5 pounds per cubic foot (pcf) is needed to maintain strength, and a core density of less than about 2 pcf is conventional for cost and insulation considerations.
Coverboards typically include fiber boards, gypsum products such as densdeck, and perlite boards. Coverboards are typically used to add integrity to the roof. For example, especially where improved fire performance is sought, the coverboard may first be applied to the steel deck, the insulation board is applied on top of the coverboard, and the membrane is then applied over the insulation board. Alternatively, especially where the roof may experience heavy traffic, the insulation board may be applied to the roof deck, the coverboard applied over the insulation board, and then the membrane is applied over the coverboard. In the latter situation, the coverboard obviously provides protection to the insulation board, which is prone to denting or damage due to the fact that the insulation boards are low density cellular materials.
Coverboards are also extensively used in re-roofing situations. In these applications, the coverboard may be referred to as a “re-coverboard.” As with residential roofs, flat or low-slope roofs can be re-roofed without removing or “tearing off” the existing roofing membrane. In many instances, the re-coverboard is first applied to the existing roofing membrane before a new roofing membrane is applied to the roof. Also, an additional layer of insulation board can be applied before the new membrane is applied. Depending upon the result desired, the re-coverboard can be applied above or below the insulation board.
In other instances, a composite board is employed in lieu of (or possible in addition to) the coverboard and insulation board. The composite boards include an insulation layer together with a layer that is rather robust such as a wood fiber, gypsum, or perlite board. One advantage of the composite board is the ease of installation. In other words, rather than apply both an insulation board and a coverboard, the composite board can simply be installed in a one-step process. Other advantages have been observed based upon the fact that the composite board is formed integrally within a controlled environment (i.e., the factory).
The use of construction boards in new roofing systems and re-roof situations is, therefore, technologically important thereby necessitating further advancement in the field.